Just bought a new X9 2010 rear mech. I use a 12-28 cassette which i guess is a relatively small largest sprocket. As a result the upper jockey wheel is no where near the 28 sprocket in the lowest gear and certainly not the stated 6mm. Adjusting the b-screw just seems to move the mech backwards and forwards beneath the 28 sprocket and not any closer. Is it better to have the b-screw wound out resulting in more chain wrap or wound in? Does it really matter?

Any help appreciated.